1. Field of the Invention
The present invention relates to a wireless communications device and a controlling method thereof, and more particularly to a wireless communications device operated as a slave that is capable of temporarily stopping an operation during an estimated communication pause period with a master.
2. Description of the Related Art
Generally, a portable wireless communications device uses a battery for power supply. Accordingly, the device can only be used for a limited time due to the limited power of the battery.
Research has been continuously performed into ways of extending the use time of portable wireless devices, and also into ways of reducing the size of the device for higher portability.
For example, one body of research suggests reducing the power consumption of the individual elements used in the wireless device, thereby reducing the power consumption of the device overall. This suggestion, however, has little advantage since not much power can be saved by current technology.
Meanwhile, another body of research underway is that of enhancing the charging efficiency of a battery by increasing the charging density without increasing the size of the battery, again with little success yet.
Since reducing the power consumption of the individual elements, or enhancing the charging efficiency of the battery are limitative and slow in developing, various methods are currently developed to reduce power consumption by controlling the operations of the communication device.
The controlling operation with respect to the communication device, for reducing power consumption, will be described below, taking Bluetooth communications as an example.
Generally, Bluetooth is a communication technology for transmitting data such as voice and video data within a distance of 10 m to 100 m at maximum speed of 1 Mbps. The Bluetooth devices that intercommunicate according to the Bluetooth standard are communicably connected with each other by processes like Inquiry, Inquiry Scan, Page, and Page Scan, or the like. According to respective roles in a network, the devices are determined to be a master or a slave. A piconet is constructed in such a manner that more than one slave is connected to one master.
A master and slaves perform bi-directional communication by a Time Division Duplex (TDD) technique.
According to the Bluetooth communication standard presently available, seven slaves can be actively connected to a master in a piconet for a mutual communication therebetween.
Once the slaves are connected to the master, the slaves can be operated in active, sniff, hold, or park modes.
Operations of the slaves in the respective modes will be described referring to FIGS. 1A through 1C.
First, referring to FIG. 1A, when the slave is in an active mode, the master sequentially transmits data to the slaves at predetermined slot intervals according to a predetermined link order. Here, reference characters M followed by increasing numeral subscripts are master-to-slave slots for the slaves of the corresponding link order.
The slave in the active mode receives data from the master during master transmission sections. If the data is addressed to the slave, the slave transmits data during the slot that is allocated after the master transmission section. In FIG. 1A, reference characters S followed by increasing numeral subscripts are slave-to-master slots for the slaves of corresponding link order.
In the active mode, the slave of zero link order, i.e., an active slave 0 receives the data addressed to the slave from the master, and transmits data during the slave-to-master slot (S0 in FIG. 1A). Then the slave is turned to reception mode, where the slave detects if the data addressed thereto is transmitted from the master. Here, the hatched portions of FIG. 1A are where the power is consumed for data transmission/reception. Since the active slave 0 needs to be operated in the reception mode even when data is transmitted from the master to the other slaves, unnecessary power is consumed.
Meanwhile, the activity time of the slaves for data transmission/reception in sniff mode is less than the activity time consumed by the active slaves, and the operation of the sniff slaves is shown in FIG. 1B.
As shown in FIG. 1B, a slave in a sniff mode, i.e., a sniff slave 1, communicates with a master after a predetermined offset (Dsniff) time and during a period of Nsniff_attempt of a sniff period (Tsniff).
Meanwhile, a slave in a hold mode, i.e., a hold slave 2 temporarily holds data transmission for a hold timeout duration, the time duration agreed with the master, and is turned to the active mode.
Lastly, as shown in FIG. 1C, a slave in a park mode, i.e., a parked slave 3, receives a slot broadcasted from the master for a beacon instant (TB), which starts at an interval of one or more beacon instants (TB). The parked slave 3 is turned into the active mode upon receiving an unpark message in a Scan section. When an unpark message is not received, the parked slave 3 remains in a sleep mode.
In order to minimize power consumption and optimize data processing by a dynamic power control using the sniff, hold, and park modes, necessary conditions for determining an optimum mode for the master and the slaves need to be regularly checked. That is, to identify necessary conditions for determining the optimum mode, such as communication traffic requested by the slaves and communication service types like voice communication or data communication, frequent communications between the master and the slaves are required. Accordingly, in addition to the time for data transmission, the time should be allocated for mode determination, and the efficiency of data transmission is deteriorated.